Ignition system development for spark ignited engines has resulted in the design of various breakerless ignition systems wherein mechanical breakers are replaced by solid state electronic switches controlled by a trigger signal. These systems are not subject to the mechanical wear and deterioration to which mechanicl breaker systems are normally subjected and consequently, the solid state breakerless ignition systems are generally more reliable.
Capacitive discharge distributor-less ignition systems have been developed for use with internal combustion engines of all sizes from single cylinder to multicylinder engines, but extensive use of these ignition systems has been made with small internal combustion engines having two, three or four cylinders. In these small engines, it is often desirable to regulate engine speed to prevent the existance of an overspeed condition, but often the costs involved in providing additional engine governing equipment are not warranted.
In internal combustion engines employing a capacitive discharge ignition system, it is desirable to provide structure which will inhibit the engine from rotating in the reverse direction. This has been accomplished in the past through the use of trigger pulse forming pulser rotors of a type illustrated by U.S. Pat. No. 3,741,185 to Thomas E. Swift et al constructed of three elements to provide a rotor having a tapering cross-section. Another non-symmetrically formed pulser rotor is disclosed by U.S. Pat. No. 3,799,137 to K. Reddy wherein the rotor has a periphery formed substantially as a convolution of a spiral. These patented pulser rotors alter the trigger pulse which is normally provided to a capacitor discharge ignition system when the internal combustion engine rotates in a reverse direction, thereby disabling the ignition system. However, these non-symmetrical pulser rotors result in rotor imbalance which increases the wear of the mechanical parts associated therewith.
Prior pulser rotors have normally been mounted upon aluminum flywheels which do not provide a good path for magnetic flux. This requires that a strong magnetic source be provided by the rotor if effective triggering pulses are to be generated. To alleviate this difficiency, some rotors have been mounted upon flux conducting flywheels, but additional flux conducting spider assemblies have been necessitated to complete a flux path between a trigger coil and the flux conducting flywheel. These spider assemblies contribute both added bulk and expense to the trigger pulse generating unit.